Heat exchangers typically include a pair of header tanks (an upper and a lower header tank) and a bundle of a plurality of pipes which link the pair of header tanks in fluid communication. Alternatively a plurality of fin members are attached to the pipes and disposed within the intervening spaces defined between the adjacent pipes of the bundle of pipes. These fin members may be fixed to the pipes either lengthwise or transversally. They may be corrugated. Heat exchangers of the type just described are disclosed in EP-A-0 745 821.
The heat exchangers of the type just described are normally made of a metallic material, usually steel, aluminium, copper or other metallic material according to the fluid used inside and/or outside the pipes. In the manufacture of such heat exchangers the pipes, header tanks, fin elements and other metallic pieces, if any, are usually first manufactured separately and thereafter assembled and attached to each other by a brazing method. More particularly, the pipes ends are inserted in corresponding holes of the header tanks and welded or brazed to said header tanks.
A known method for manufacturing heat exchangers in mass production includes successively a step of assembling the metallic components of the heat exchanger, a step of spraying a flux with an electrostatic flux delivering apparatus, a step of thermal degreasing in an oven to vaporize oil and grease present on the metallic elements and a step of brazing. This step of brazing comprises conveying the heat exchanger assembly on a close loop belt conveyor through a brazing furnace containing a nitrogen atmosphere.
This known method is usually used in the mass production of heat exchangers for the automotive industry (specially the car industry) and also for the home and industrial air conditioning industry.
It necessitates the use of heavy machinery having a high production output but with the disadvantage of a very limited flexibility, a very limited process ability, a long process time and an important energy consumption. This important energy consumption is particularly inherent to the use of a long oven which has a very high thermal inertia and which has thus to be maintained at high temperature during a prolonged time even when it does not contain heat exchangers assembly for a moment. The close loop belt conveyor is another source of heat loss, because this belt conveyor is first heated when passing through the oven and thereafter cooled when moved out of the oven.
Another disadvantage of this known method is the huge brazing line which is normally not less than 50 m for a height of 4 m. In the best case, starting with a heat exchanger pre-assembly, it takes more than one hour to produce a brazed heat exchanger ready for use.
This production line is further noisy, which constitutes a further disadvantage.
A still further disadvantage of this known method is its important investment cost.